Today's communication environments may comprise a plurality of access networks having different communication capabilities and covering different geographical areas. For example, a communication environment may comprise a Wireless Local Area Network (WLAN) and a W-CDMA network, wherein the W-CDMA network may have different communication capabilities than the WLAN network. Also, the access networks may partly overlap each other or one access network may as a whole overlap the other access network. In such a communication environment, there may be occasions when a network connection of a mobile communication node, such as a laptop computer having communication means, needs to be moved from one access network to another access network, i.e. when the network connection needs to be handed over from e.g. the W-CDMA network to the W-LAN network or from one W-CDMA network to another W-CDMA network. This may be necessary because e.g. the mobile node has moved geographically such that the access network with which it originally communicated experiences bad communication capabilities, e.g. bad radio coverage. Another reason may be that the user of the mobile node has changed its way of communicating such that it needs another quality of service, which is better taken care of by another access network. Such a handover between access networks is called network layer handover.
Mobile IPv6 and Mobile IPv4 are prior art network layer mobility management protocols enabling such mobility in IPv6 and IPv4 based networks, respectively. Mobile IPv6 is described e.g. in the document “Mobility support in IPv6” by Johnson et al, RFC3775, published on the Internet by the Network Working Group of the IETF in June 2004. This document specifies a protocol which allows mobile communication nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identifiable by a home address, i.e. a static IP address of the mobile node valid at the mobile node's home network, regardless of the mobile node's current point of attachment to the Internet. When situated away from its home network, i.e. when connected to the Internet via a foreign access network, the mobile node is also associated with a care-of address, which provides information about the mobile node's current location. A care-of address is a temporary IP address of the mobile node valid at the foreign access network that the mobile node visits. The care-of address is registered in a binding update list in a home agent in the home network as an association with the mobile node's home address. A “binding” means an association of the home address with a care-of address, and a home agent is a router located at the mobile node's home network that is used by the mobile node for registering its care-of address. Thereby, IPv6 data packets addressed to the mobile node's home address can be transparently routed to the mobile node's care-of address.
For a mobile node in a Mobile IPv6 based system to perform a handover from one access network to another access network, the mobile node collects information relevant for making a handover decision from the available access networks, such as radio link quality measures of the radio links between the mobile node and access points in the available access networks. The mobile node evaluates the information relevant for making a handover decision, and makes a decision to handover the connection to another access point in another access network, e.g. when the current radio link quality goes below a certain threshold and a radio link quality of an access point in another network is above a certain threshold. Then the mobile node will configure a new care-of address valid in the new access network. The new care-of address may be communicated to the mobile node from the new access network. Thereafter, the mobile node performs the handover by:    sending a Binding Update message to the home agent, instructing the home agent to associate the home address with a new care-of address, and    receiving a binding acknowledgement message from the home agent, after it has successfully received and processed the binding update message.
The Mobile IPv6 also enables correspondent nodes, i.e. other communication nodes, such as computers, that are communicating with the mobile node, to send packets destined for the mobile node directly to its care-of address. If this routing optimisation opportunity is used, the mobile node will also send Binding Update messages directly to the correspondent nodes, including the mobile node's care-of address associated with the mobile node's home address.
The mobile IPv4 protocol is described e.g. in. “IP Mobility Support for IPv4” by Perkins et al, RFC3344, published on the Internet by the Network Working Group of the IETF in August 2002. The process for achieving mobility in an IPv4 based system is similar to the process for an IPv6 based system.
The Host Identity Protocol (HIP) is another network layer mobility management protocol for achieving mobility between access networks in an IP based communication environment. HIP is described e.g. in “End-Host Mobility and Multi-Homing with the Host Identity Protocol”, draft-ietf-hip-mm-01, by Nikander et al, published by the IETF in Feb. 20, 2005 as an Internet draft, which is a working document. The HIP defines a mechanism that decouples the transport layer (TCP, UDP, etc) from the internetworking layer (IPv4 and IPv6). When a host (which is similar to a mobile node) uses HIP, the overlying protocol sublayers are not bound to IP addresses but instead to Host Identifiers. A host, or mobile node, is identified by its Host Identifier and located by its IP address, i.e. when moving to a new network it gets a new temporary IP address but keeps its Host Identifier. Thereby, HIP also makes it possible to make handovers between IPv4 and IPv6 addresses, i.e. between an IPv4 based network and an IPv6 based network. In HIP a “rendezvous” server is described which corresponds to the Home Agent in Mobile IP.
In solutions based on network layer mobility management protocols, such as the above described Mobile IPv4, Mobile IPv6 and HIP, all control of the handovers lie within the mobile node. Although, network operators having many different access networks in their communication system would like to easily control the mobility between access networks, i.e. the network layer handovers, e.g. in order to balance the load within their access networks. This is not possible in the prior art solutions described above. To be able to control the mobility of mobile nodes between access networks by the network operators is especially interesting in modern IP networks where many communication nodes will be mobile and have multiple access network interfaces, e.g. both W-CDMA and WLAN interfaces, whereby the mobile nodes can dynamically and individually attach to different access networks based on need of the current application and/or service. Therefore, there exists a need for a solution where the network layer handovers are controlled in a communication network, e.g. by a network operator.
In the document “Motivation for network controlled handoffs using IP mobility between heterogeneous Wireless Access Networks” by Njedjou et al, published by the IETF in June 2003 as an Internet draft, which is a working document and which validity has now expired, the desirability of a network controlled handover process is discussed. In this document a new function in the home network is introduced called a Mobility Manager that gathers information from the involved access networks, transfers the information to the mobile node such that the mobile node takes handover decisions which are based on the information received from the mobility manager, as well as on information of radio link characteristics and the need of the current application and/or service.
In this prior art solution the mobility management decisions, i.e. the handover decisions are made within the mobile nodes. This would require a lot of processing in the mobile nodes. Further, a lot of signalling is required to receive information from the access networks and to send information to the mobile nodes. Further, all this processing and signalling over a radio interface need to be secured somehow causing even more processing needs. Also, since the handover decisions are still made within the mobile nodes, the access networks, and the network operator of access networks in a communication environment will not have a full control of the usage of its access network resources. The network operators can supply a mobile node with information that would advice the mobile node to e.g. handover to a certain access network, but since the handover decisions are still made in the mobile device the network operators cannot force the mobile node to do such a handover. Therefore, there still exists a need for a solution that improves the possibility to control access network resources from a communication network in a communication environment comprising a plurality of access networks.